Process for tanning and impregnating materials by means of electricity.



B. SCHWERIN.

PROCESS FOR TANNING AND IIVIPREGNATING MATERIALS BY MEANS OF ELECTRICITY.

APPLICATION FILED SEPT.8. I914.

Patented June 5, 1917.

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115111 2 1 om 3 2? I I UNTED @TATES PATENT @FFTCE BOTHO SCHWERIN, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR TO ELEK- TRO-OSMOSE AKTIENGESELLSCHAFT, LIN, GERMANY, A CORPORATION.

(GRAF SCHWERIN GESELLSCHAFT,) OF BER- PROCESS FOR TANNING AND IMPREGNATING MATERIALS BY MEANS OF ELECTRICTTY.

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Specification of Letters Patent.

Application filed September 8, 1914. Serial No. 860,731.

To all whom it may concern:

Be it known that LBOTHO SCHWERIN, a subject of the German Frankfort-on-the-Main, Germany, have invented certain new and useful Improvements in Processes for Tanning and Im regnating Materials by Means of Electricity, of which the following is a specification.

This invention relates to a process for tanning, impregnating, dyeing superficially or throughout and like treatment of materials with aid of electricity. Byway of illustrating the invention there is described in the sequel its application to tanning skins or hides with tannin, though it is applicable, so far as the art of tanning is concerned, also when other tanning agents, such as quebracho or chromium compounds are used.

The invention utilizes the fact that a tanning liquor may be carried through the hide by the electric current, that is to say electro-osmotically, whereby the hide is able to take up the tannin and become converted into leather.

Many processes have been proposed for tannin with aid of electricity, but hitherto none 0 these has come into practice. The reason is that the tanning operation has always been attributed to a purely chemical operation, for instance to the action of nascent hydrogen and oxygen; or that, although the possibility of electro-osmotic treatment has been recognized, the conditions suitable for electro-osmosis have not been attained. It has been proved that tannin is decomposed by the electric current, but a suitable counvteracting agent has not become known.

Finally, the most obvious expedient for preventing such decomposition, namely the use of alternating current, is inimical to electroosmosis.

The present invention avoids all the phe nomena which hinder the attainment of the object in question and provides a practicable and rapid tanning process,

The transport of the active substance, in this case tannin, into or through the material, in this case skin or hide, under, treat ment is effected by subjecting the material and the liquid containing the active substance to the action of the electric current between diaphragms. When operatingwith a liquid free from substances that hinder Emperor, residing at electro-osmosis, the material to be tanned or impregnated may be suspended on the Walls wlthin the space between the diaphragms without tight inclosure and the circulation of the liquid may be aided by stirring 01- stituents which injuriously affect the electroosmosis are those electrolytes which check or entirely prevent the migration of the tannin. The process may be so conducted that before the actual tanning, impregnation or .the like, the substances which hinder or pre vent the .operation are removed from the material by electro-osmotic 'de-adsorption and an .electrical charge of character corresponding with the active constituent impart ed to the material. The material is then preferably arranged as a partition dividing the space between the diaphragms, when it acts ltself. as a diaphragm and permits migration of the active substance. For example, in tanning hide with tannin an electropositive character should be imparted to the hide, when tanning with chromium compounds.

By observing these conditions the tannin solution can be caused to migrate electroosmotically through the hide, whereby the latter becomes leather, the degree of tannage being apparently dependent on the concentration of the liquor and on the tension of the electric current used.

The special case of tanning hide with tannin will be further explained. The hide is assumed to have been plumped with lime. '-In the drawings, Figure 1 is a vertical section through a'receptacle for holdin the liquid, showing diaphragms mounted t erein; Fig. 2 is a plan view; Fig. 3 is a vertical section at right angles to the section of Fig. 1, and showing a hide stretched in a frame.

In the several views, dis a vessel of suitable form, subdivided namely by the diaphragms 5, 6 into a middle and an electronegative character into 4 compartments,

compartment and two side compartments,

the middle compartment being further subdivided into compartments 2 and 3 by the hide 7 which is stretched in a frame either directly or with use of a support. Behind the diaphragms are arranged the preferably perforated poles 8 and 9, in such a manner that they are in contact with the diaphragms. The latter may consist of a cellulose preparation, like parchment paper or viscose. The cathode chamber 1 and the anode chamber 4, are filled .with water, which, in order to avoid resistance, preferably contains traces of caustic soda in the cathode chamber and of sulfuric acid in the anode chamber. In the anodic middle chamber there is water, in the cathodic middle chamber a dilute acid suitable for de-liming hide. When the electrodes are connected with the poles of a source of electric current, the hide is first purified in that the lime and other basic residues migrate out of it and pass into the cathode chamber through the feebly negative diaphragm. By this treatment the hide come gradually of stronger electro-positive character. The first stage of the treatment is at an end when the de-adsorption of the basic residues is complete.

The tanning liquor is now charged into the chamber in front of the cathode. By the action of the electric current those cathodic constituents which could hinder the osmosis migrate through the cathodic diaphragm. On the other hand, the negative ions which prevent or limit the migration of the tannin migrate first through the hide and then into the anode chamber through the indifferent diaphragm.

Proportionally to this progressive puri-' fication of the tannin liquor, the solution of the tannin migrates through the hide and appears in the middle chamber 3, whence the solution is withdrawn. After it has been replenished it can be used again. This has the advantage that the longer the tanning liquor is used the purer it is.

The anodic diaphragm must have such a potential thatthe actual ions can migrate through it, while the tannin cannot. If

ure tannic acid solution, which contains no ions that can hinder osmosis, is used from the beginning, the hide need not be stretched in the middle chamber but merely suspended therein. Circulation of the tanning liquor by stirring is then permissible.

Ifan impure tanning liquor contains acid residues, the osmosis of the tannin solution will not occur until the acid residues have passed the hide in order to be separated by the anodic diaphragm. If now by stirring the acid residues are again brought around to the cathode side, the migration of the tannin solution and therefore the tanning will be' 55 more or less delayed. So also basic residues is caused to fall, and at the same time to bewhich are brought by stirring tothe anode side of the hide, act to diminish the electric charge of the hide by back-migration, and this is obviously accompanied by a delay of the migration of the tannin. In impure tannin solutions, therefore, the hide must be stretched.

The following experiment may be cited A goat skin was stretched in the osmose apparatus shown and subjected to osmosis by a tannin solution of 5 per cent. strength from the cathodic middle chamber. After about 5-10 minutes the tannin could be detected in the anodic middle chamber. In about half an hour the skin was fully tanned. The liquid transferred by cataphoresis from the cathodic to the anodic middle chamber amounted to about 500 cc. per hour. The necessary current data are on an average 1 ampere at 100 volts per square decimeter of anode surface.

The general applicability of the facts on which this new process is based permits of its general use. All problems may be solved by it, which relate to the introduction into certain materials electro-osmotically of other constituents under like experimental conditions, for example in cases of adsorption,

dyeing superficially or throughout, tanning and impregnatmg.

Having thus described the nature of my said invention and the best means I know of carrying the same into practical effect, I claim 1. A process for introducing a substance into or onto a material, which process consists in confining the material and a liquid containing the substance in question between diaphragms of such electric charge that they permit migration through them of constituents of the liquid which injuriously affect electro-osmosis while retaining the substance in question, and passing an electric current through the liquid and diaphragm.

2. A process for introducing a substance 1 into or onto a material, which process consists in first separating electro-osmotically by de-adso'rption from the material constituents which hinder the introduction and then confining the material and a liquid contain- 5 ing the substance in question between diaphragms and passing an electric current through the liquid and diaphragms.

3. A processof introducing a substance into or onto a material, which process .con- 2 sists in confining the material as a partition dividing the space between diaphragms in a bath of liquid containing the substance in question, and passing an electric current through the liquid and diaphragms.

4:. The process herein described which con sists in introducing water into the chamber of a receptacle between one side of a hide disposed therein and a diaphragm of cellulose or the like, introducing dilute acid into a chamber between the hide and a negative diaphragm passing a direct current between the diaphragms and causing the hide to become more strongly electro-positive, the basic residues passing through the negative diaphragm, charging a tanning liquor into a chamber between the cathode and the Wall of the receptacle, causing the cathodic constituents to migrate through the cathodic diaphragm and the negative ions to migrate through the hide and the diaphragm first mentioned, and the tanning liquor to pass through the hide, and finally withdrawing the liquor from the chamber between the hide and the diaphragm first mentioned.

In testimony whereof I affix my signature in presence of two witnesses.

BOTHO soHW RiNL Witnesses JEAN GRUND, CARL GRUND. 

